How many people have so many opinions. Many people think that Bitcoin should be official and somebody is absolutely against it.

It is your bitcoin don't let him do things that you don't have or don't think is needed because if your heart doesn't want to sell bitcoin then follow your instincts that is not a true friend if they want you to do what they want. I think your friend just want shares from your bitcoin.

explain to them about the advantages and disadvantages if you sell your bitcoin now so they will understand for the reason that you hold bitcoin until the price you want

Perhaps those who advise you to immediately sell you Bitcoin because they have see it was falling, are not truly understand the world of crypto currencies, they really want to help in a sense that they want to stop lose. However, you have to keep in your mind that you may lose once you sell.

You can simply explain the brief history of Bitcoin and the market.

I am not here to stop your decision, it was your free choice.

Honestly you do not have to listen or explain anything to him.  It is your coin and he has nothing to do with it.  Instead, ask him to explain why he said it so.  If you do not want to sell your coins, do not sell it.  He should be the one that do the reasoning and explaining because it is out of his league since that Bitcoin is yours.

do not sell your coins now unless it is a bullshit coin. The market will recover soon after few next weeks. you must have your own decision. do not believe anyone

An advise is defined as "giving an opinion that is worth following". Despite its definition, I believe that at the end of the day the decision on when to take that advise is still dependent on what you decide to do. Receiving an advise doesn't mean that you are obligated to follow it, instead you have a choice to thin it through and weigh your options as to what the circumstance allows. Knowing that it's your coins on the line, the most important opinion on what action to partake is yours so think it through and decide for your own. If you think that the opinion is valuable then consider it but remember that you are not obligated to follow by what other thinks that are against what you want. Your coins, your rules.

Is you friend a financial expert or has made better financial decisions than you in the past ? If the answer to this is no, you need not hear his advice. It is better if you even do not talk about money and finance with friends until extremely needed. his can ruin the complete relationship.

You should make decisions regarding buying and selling your coins based on your research or advice from experts who have already made good decisions in the past. There are a lot of experienced members here who keep sharing tips on what is the right time to sell your current holdings for maximum profit. 

Maybe your friend doesn't want you to lose more value of bitcoin because he felt that the bitcoin price will still go down. But it is really up to you because you are the one holding it. Whether you want to keep it expecting that the price could still go up or follow your friend's suggestion. For me I will still hold in my bitcoin because I believe its price will go up again.